1. Field of the Invention
The present invention relates to a robot apparatus including a multi joint arm having a plurality of joints and to a controlling method of the robot apparatus.
2. Description of the Related Art
Conventionally, a robot apparatus is widely used, the robot apparatus including: a multi joint arm and an end effector (hereinafter, called “robot body”); and a control apparatus that controls the robot body. In general, the robot body includes a drive mechanism, such as a motor, and a transmission mechanism, such as a timing belt and a pulley. The drive mechanism including the motor and the transmission mechanism generate heat due to heat loss or friction during operation, and the mechanisms act as heat sources. Therefore, if the robot body is operated for a long time, the robot body enters a state (hereinafter, called “warmed-up state”) in which the temperature is ten to several dozen ° C. higher than when the robot body is stopped.
In a production line provided with the robot body, there may be cases in which the operation of the robot body needs to be suspended even though the operation is possible, such as during maintenance, during off-hour stop and during temporary stop due to some reasons. The robot body does not generate heat in the operation stopping period, and the robot just after the operation is resumed is in a state (hereinafter, called “cooled state”) in which the temperature is lower than in the warmed-up state.
It is known that if the robot body is operated under different temperature conditions such as the warmed-up state and the cooled state, the stop position of the robot body and the amount of errors at deceleration stop slightly vary between the states, and the motion accuracy of the robot body is reduced. Turning the robot body from the cooled state to the warmed-up state may take two to four hours after the start of operation, and for example, the motion accuracy of the robot body is reduced in 25 to 50% of the operation hours when the operation is eight hours a day. There is a problem that the work efficiency may be reduced.
To solve this, Japanese Patent Application Laid-Open No. 2008-235839 discloses a robot apparatus including a heater and a temperature sensor on the robot body, wherein the heater can heat the robot body. According to the robot apparatus, the robot body is mandatorily heated, and the temperature of the robot body is controlled at a suitable temperature in a feedback control using the temperature sensor, thereby reducing the time for switching the robot body from the cooled state to the warmed-up state.
Japanese Patent Application Laid-Open No. 563-127885 describes a robot apparatus including a temperature sensor on the robot body, wherein the amount of heat generation can be increased by adjusting a d-axis current to perform a vector control of a driving brushless motor. According to the robot apparatus, the d-axis current is adjusted to heat the robot body, and the temperature of the robot body is controlled at a suitable temperature in a feedback control using the temperature sensor, thereby reducing the time of switching the robot body from the cooled state to the warmed-up state.
However, the temperature sensors are mounted on the robot apparatuses described in Japanese Patent Application Laid-Open Nos. 2008-235839 and S63-127885. Therefore, there is a problem that the mechanism and the controlling system are complicated, and the cost of the robot apparatus is high. The setting temperature in the heating control of the robot body is not particularly taken into account. Therefore, there is a problem that the consumption of energy may be excessive due to an unnecessarily large amount of heat generation, or the heat generation may be insufficient.